1. Field of the Invention
The present invention relates to the storage and retrieval of stackable products and particularly to facilitating the temporary storage of products, reels of packaging material for example, which have a high turnover frequency. More specifically, this invention is directed to a storage system which comprises a plurality of endless conveyors, arranged horizontally one above the other in plural storage tiers, and especially to such a storage system which includes the capability of simultaneously delivering products to storage and extracting products from storage for consumption. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
"High-shelf" storage units are known in the art. An example of such a prior art storage unit may be seen from published German application DE-A-3,234,817. The prior art "high-shelf" storage units, as exemplified by the referenced German application, employ vertically movable carriers for transferring products to and from the storage "shelves". These vertically movable carriers are also movable along the length of the storage unit. The "shelves" of the storage unit of the referenced application are in the form of horizonally arranged rotary conveyors. These rotary conveyors receive the in-coming products from the vertically movable carriers and, upon extraction of the stored products from the storage unit for use, they must be returned to the carriers. Thus, the products, typically resting on pallets or the like, will be supplied on a first conveyor, stored, subsequently extracted from storage, and removed from the storage unit on a second conveyor.
A long standing disadvantage of the prior art high-shelf storage units, as exemplified by the system of the referenced German application, resides in the fact that the access times to the stored products are relatively long. Accordingly, product throughput and availability is relatively low. This low throughput and availability is primarily attributable to the fact that the loading of products onto the shelves of the storage unit and the subsequent unloading step is accomplished by means of the same horizontally and vertically movable carriers. Also, the prior art has not met the demand for storage units which are as small as possible, i.e., storage units characterized by high volumetric efficiency, and which can accommodate a high turnover frequency and thus minimize stock requirements. As a further disadvantage of the prior art, the previously available high-shelf storage units were not well suited for use in the temporary storage of different products for which there were differing demands.